The present technique relates to transition detection circuitry, and to a method of detecting a transition of a signal occurring within a timing window.
Transition detection circuits can be used for a variety of reasons within modern data processing systems. A transition detection circuit is used to detect a transition in an input signal to the transition detection circuit that occurs within a predetermined timing window, and in the event of detecting such a transition the transition detection circuit typically issues an error signal. The transition detection circuit may be arranged to detect a rising edge transition (a logic zero to logic one level transition), a falling edge transition (a logic one to logic zero level transition), or both.
It is known to employ margining methods during the timing analysis and sign off of a data processing system design in order to account for variations such as process, voltage and temperature (PVT) variations. However, whilst such margining methods make the data processing system design robust against timing failures, they can have a significant impact on performance and energy consumption. Accordingly, there has been much interest in developing adaptive techniques that seek to eliminate a significant portion of safety margins by dynamically adjusting system parameters such as supply voltage, body bias and operating frequency to account for variation in environmental conditions and silicon grade.
To seek to eliminate worst-case safety margins, ARM Limited developed a voltage and frequency management technique for Dynamic Voltage and Frequency Scaled (DVFS) processors, based on in-situ error detection and correction, called Razor. The in-situ error detection circuitry within Razor can be arranged to use the earlier-mentioned transition detection circuitry in order to identify when data signals are transitioning too close to a clock edge identified by the timing window, indicating a timing error. In such instances, an error signal can be issued, and corrective actions can then be taken. Significant energy savings can be realised using such techniques, by removing the margins traditionally provided for PVT variations, and even by deliberating tolerating a targeted error rate, allowing for example the supply voltage to be scaled even lower to provide additional energy savings.
Transition detection circuitry can also be used in other situations. For example, such a transition detector can be used to monitor aging of a data processing system. In particular, as the device ages, certain components will operate more slowly, which may result in late transitions in signals, that can then be detected by such transition detection circuits. Such transition detection circuitry can also be used for example to detect transient event upsets, that may cause a late transition in a data signal.
Transition detection circuits typically operate by generating a pulse from a rising or falling transition in an input signal, and an error signal is then flagged when that pulse is detected within a predetermined timing window. In known transition detection circuits, the pulse generator components are suitably sized to generate a wide pulse from a transition in the input signal being monitored. A wide pulse ensures that robust error detection can be achieved even under pessimistic PVT variation conditions and when the monitored node glitches. However, the use of such wide devices incurs power (both leakage and dynamic) and area overheads within the data processing apparatus including the transition detection circuit. These overheads can limit the energy-efficiency gains achievable through adaptive technique such as Razor, and will ultimately limit the total number of signals that can be monitored using such transition detection circuitry, especially in a balanced pipeline design. In addition, the wide pulse can cause early transitions (that would in fact not be problematic) to be flagged as timing errors (this early detection of timing errors being referred to as the set-up pessimism of the transition detector).
Accordingly, it would be desirable to provide an improved transition detection circuitry that enables the above problems to be alleviated.